In the manufacture of semiconductors such as LSI and VLSI and the manufacture of liquid crystal displays and the like, patterns are formed by irradiating light onto a semiconductor wafer or a liquid crystal original plate; however, if dust adheres to the photomask or the reticle (hereinafter simply referred to as a “photomask”) used on these occasions, there occurs a problem of impaired dimensions, quality, and appearance, due to roughened edges or black stains on the base.
For this reason, these operations are usually performed in a clean room, but it is still difficult to keep the photomask constantly clean; so light exposure is carried out after attaching the pellicle as a dust fender over the surface of the photomask. In this case, a foreign matter does not directly adhere to the surface of the photomask but adheres to the pellicle; so if the exposure light is focused on the pattern described on the exposure original plate the foreign matter stuck on the pellicle does not partake in the image transferring.
Generally, a pellicle is formed by adhering a transparent pellicle film made of nitrocellulose, cellulose acetate, fluorine-including resin or the like which permits light to pass well to an upper end face of a pellicle frame made of aluminum, stainless steel, polyethylene or the like, said adhesion being effected by first applying a solvent which dilutes the pellicle film well to the upper end face of the pellicle frame, air-drying the solvent and then bonding the pellicle film to it (see IP Publication 1), or in place of the solvent an adhesive such as acrylic resin or epoxy resin is used for the bonding (see IP Publication 2 and IP Publication 3). Further, on the lower end face of the pellicle frame, an agglutinant layer is laid which is made of polybutene resin, polyvinyl acetate resin, acrylic resin, silicone resin or the like for bonding the pellicle to the photomask, and also a releasing layer (separator) for protecting the agglutinant layer is laid over the agglutinant layer.
When such a pellicle is attached to the surface of the photomask, and a photoresist film formed on the semiconductor wafer or the liquid crystal original plate with this photomask is subjected to the exposure light, the foreign particles such as dust material stick only to the surface of the pellicle but not directly to the photomask so that if the focal point is controlled to come on the pattern formed on the photomask, it is possible to avoid the effect of the foreign particles.
Now, semiconductor devices and liquid crystal displays have been increasingly highly integrated and densified in recent years. At present, a technique for forming a fine pattern of about 32 nm on a photoresist film has also been put to practical use. As long as the fine-ness of the pattern is about 32 nm, it is possible to cope with the demand by means of the methods such as the immersion exposure method in which the space between the semiconductor wafer or the liquid crystal original plate and the projection lens is filled with a liquid such as ultrapure water and then the photoresist film is exposed by using an argon fluoride (ArF) excimer laser, or an improved technique which uses a conventional excimer laser to effect multiple exposure.
However, further densified pattern formation is required for next-generation semiconductor devices and liquid crystal displays, and it has proved to be difficult to form such finer patterns by merely using conventional pellicle and exposure technologies.
Therefore, in recent years, as a method for forming a finer pattern, an EUV exposure technique using EUV light having a dominant wavelength of 13.5 nm is in the light.